Many people use mobile stations, such as cell phones, personal digital assistants (PDAs), tablet computers, laptop computers, desktop computers, in-car computers, and so on, to communicate with cellular wireless networks. These WCDs and networks typically communicate with each other over a radio frequency (RF) air interface according to a wireless communication protocol such as Code Division Multiple Access (CDMA), perhaps in conformance with one or more industry specifications such as IS-95 and IS-2000. Wireless networks that operate according to these specifications are often referred to as “1×RTT networks” (or “1× networks” for short), which stands for “Single Carrier Radio Transmission Technology.” These networks typically provide communication services such as voice, Short Message Service (SMS) messaging, and packet-data communication.
Mobile stations typically conduct these wireless communications with one or more base transceiver stations (BTSs), each of which send communications to and receive communications from mobile stations over the air interface. Each BTS is in turn communicatively connected with an entity known as a base station controller (BSC), which (a) controls one or more BTSs and (b) acts as a conduit between the BTS(s) and one or more switches or gateways, such as a mobile switching center (MSC) and/or packet data serving node (PDSN), which may in turn interface with one or more signaling and/or transport networks.
As such, mobile stations can typically communicate with one or more endpoints over the one or more signaling and/or transport networks from inside one or more coverage areas (such as cells and/or sectors) of one or more BTSs, via the BTS(s), a BSC, and an MSC and/or PDSN. In typical arrangements, MSCs interface with the public switched telephone network (PSTN), while PDSNs interface with one or more core packet-data networks and/or the Internet.
To meet increasing demand for high-speed data on mobile devices, cellular service providers have begun implementing “4G” networks, which provide service under one or more 4G air interface protocols, such a long-term evolution (LTE) protocol. LTE was developed by the 3rd Generation Partnership Project (3GPP), and is based on GSM/EDGE and UMTS/HSPA network technology.
In the context of LTE, a mobile station is typically referred to as a “user equipment” (UE), and may take various mobile and stationary forms, such as a mobile phone, tablet computer, laptop computer, desktop computer, or any other device configured for wireless communication. Herein, the terms “mobile station,” “wireless communication device” (or WCD), and “user equipment” (or UE) may be used interchangeably. Further, in the context of LTE, a base station is typically referred to as an “eNodeB.” Herein, the terms “base station” and “eNodeB” may be used interchangeably.
In an ideal arrangement, the base stations of a cellular wireless system would provide seamless coverage throughout a region, so that UEs being served by the system could move from coverage area to coverage area without losing connectivity. In practice, however, it may not be possible to operate a sufficient number of base stations or to position the base stations in locations necessary to provide seamless coverage. As a result, there may be holes in coverage.
One way to help solve this problem is to install a wireless relay that extends the range of a base station's coverage area so as to partially or completely fill a coverage hole. Such a relay may be configured with a wireless backhaul interface for communicating with the base station in much that same way a UE does, and a wireless access interface for communicating with and serving one or more UEs in much the same way that a base station does. The relay may further include control logic for actively bridging the backhaul communications with the access communications. The relay may thus receive and recover downlink communications from the base station and transmit those communications to UEs, and receive and recover uplink communications from UEs and transmit those communications to a base station.
Typically, a base station with which a wireless relay communicates is referred to as a “donor base station” (or “donor eNodeB,” in the context of LTE), and the wireless relay itself is referred to as a “relay base station” (or “relay eNodeB,” in the context of LTE). A relay base station or relay eNodeB may also be referred to herein simply as a “relay node.”
Advantageously, a relay base station can have a relatively small form factor, with antenna height lower than the donor base station and with reduced transmit power requirements. Consequently, a cellular wireless service provider may conveniently employ such relay base stations throughout a region to efficiently fill coverage holes and help improve service quality.
In some cases, a wireless service provider may wish to extend coverage by installing a relay base station, which may also be referred to as a “mini-macro” (MM) base station, at a location outside of the signal range of an existing base station. To do so, the relay base station may be configured to couple (e.g., via a local area network or other wireless connection) with a UE, which may be referred to as a “relay UE,” which is served by a donor base station in much the same way that the donor base station serves other UEs.
With this arrangement, when the relay UE attaches with the donor base station, the relay UE may acquire connectivity and an IP address as discussed above for instance. But based on a profile record for the relay UE, the network (e.g., a signaling controller) may recognize that the relay UE is a relay UE (rather than a normal end-user UE) and may therefore set up a bearer connection for that relay UE with a special core network gateway system (e.g., “SAE GW”) that provides for internal core network connectivity and assigns the relay UE with an IP address for use to communicate within the core network. Once the relay UE receives that core network IP address assignment, the relay UE may then convey that IP address to the relay base station for use by the relay base station as the relay base station's IP address on the core network. The relay base station may then operate as a full-fledged base station of the network, having IP-based interfaces with other core network entities (e.g., a signaling controller, a gateway system, and other base stations), albeit with those interfaces passing via the wireless backhaul connection provided by the relay UE, and via the core network gateway system.
Once the relay base station is thus in operation, the relay base station may then serve UEs in the same way as a standard base station serves UEs. Thus, when a UE enters into coverage of the relay base station, the UE may signal to the relay base station to initiate an attach process, the UE may acquire an IP address, and an MME may engage in signaling to establish one or more bearers between the UE and a gateway system. Each of these bearers, though, like the relay base station's signaling communication, would pass via the relay's wireless backhaul connection.
Herein, the term “relay node” may be used to refer a relay base station with a direct wireless backhaul connection to a donor base station, and to the combination of a relay base station and a relay UE that provides the relay base station with a wireless backhaul link to a donor base station. Further, the wireless communication link between a relay base station or relay UE and the donor base station may be referred to as a “relay backhaul link,” while a wireless communication link between a relay base station and a UE may be referred to as a “relay access link.” Similarly, the wireless communication link between a donor base station and a UE may be referred to as a “donor access link.”
In a further aspect of some protocols, such as LTE, reception at cell edges may be problematic for various reasons. For example, the greater distance to a base station at a cell edge may result in lower signal strength. Further, at a cell edge, interference levels from neighboring cells are likely to be higher, as the wireless communication device is generally closer to neighboring cells when at a cell edge.
In an effort to improve the quality of service at cell edges, 3GPP LTE-A Release 11 introduced a number of Coordinated Multipoint (CoMP) schemes. By implementing such CoMP schemes, a group or cluster of base stations may improve service at cell edges by coordinating transmission and/or reception in an effort to avoid inter-cell interference, and in some cases, to convert inter-cell interference into a usable signal that actually improves the quality of service that is provided.
LTE-A Release 11 defines a number of different CoMP schemes or modes for both the uplink (UL) and the downlink (DL). For the downlink, there or two basic types of CoMP modes: coordinated scheduling/beamforming (CSCH or DL-CSCH) and joint processing. When coordinated scheduling/beamforming is implemented for a given UE, data is only sent to the given UE in one cell at a time, but scheduling and beamforming decisions for the given UE are coordinated amongst multiple cells. When a type of joint processing referred to as joint transmission is implemented for a given UE, data is transmitted to the UE in multiple cells concurrently. Other types of CoMP schemes on the uplink and downlink also exist.